Pad and Fan Evaporative Cooling

Fan and Pad Evaporative Cooling

Fan and pad evaporative cooling is one of the most common cooling process used in greenhouses. The components of this process include a cellulose pad, overhead water supply tubing, a reservoir or gutter to collect excess water, a sump tank, a pump, piping and controls. These parts create a complete system that cools a greenhouse.

The process used in pad and fan cooling is similar to direct cooling. The first part of the process is making sure the pad is installed along a wall/side that is opposite the fans. The pad is soaked by the overhead water supply pipe. Once drenched, the pad has an air supply blown across it, and passed through exhaust fans. Unused water is collected below in a reservoir or gutter to the sump tank.  The water returning to the tank is filtered, and re circulated to the top to redrench the water.


The pad-and-fan system contains many different variables in factoring how the system works.  These can include pad size, water supply, sump capacity, controls, equipment, and coolers/chillers.  Below is a description of each variable and ideas to keep in mind.

Pad Size– normally airflow rate is 8 cubic feet per minute per square foot

Can be modified for unshaded greenhouses

Airflow rate is total fan capacity needed and supplied to .1” of water static pressure

Height should be no less than 2’ and no greater than 8’

Water Supply- Make sure pads are not a solid wall of water

Differs upon cellulose of pad

Large system may need to require several pumps

Should be sized for 1 gallon/minute per 100 square feet of pad area

Sump Capacity – can be a tank or modular unit

Needs to be large enough to supply the pump

Controls– fan and pad system is activated at last stage of cooling

Controlled by a thermostat, controller or computer

Humidistat controls the humidity

Evaporative Cooling System- self-contained units

Usually mounted outside on wheels/walls and uses a hose and has an electrical connection

Placed near a door at end of greenhouse opposite the fans

Uses nozzles mounted outside of green house

Exhaust opening is used by the door, roof vent, or shutter to release warm air


Whaley Products

SA Series
Packaged Chillers
(integrated pump tank)
1.5Ton – 20Ton
Single / Dual Circuits
Single / Dual Pumps
SAE Series
Modular Chillers
(pump & tank on
separate skid)
1.5Ton – 200Ton
Single / Dual Circuits
SAR Series
Split Chillers
(Outdoor Condensing Unit)
(pump, tank, evaporator on
indoor skid)
1.5Ton – 200Ton
Single / Dual Circuits